1. Field of the Invention
This invention relates to films of polymeric acrylonitrile. More particularly, the invention relates to polyacrylonitrile films and to a method of their preparation, which films are characterized by extremely high tensile strength and stiffness, and by outstanding gas barrier properties. The invention also relates to films of acrylonitrile polymer-water, the water being present within the film in an amount of at least 20% by weight, such films being highly fire resistant.
2. Description of the Prior Art
Although polyacrylonitrile has been known and available since the later 1940's, it has not been successfully utilized commercially in film form, probably because of its "intractability", in that it cannot be melted without decomposing, so that conventional hot melt extrusion techniques are simply inapplicable.
Shaped articles of polyacrylonitrile have been described in prior patents. See, e.g., U.S. Pat. Nos. 2,858,290 and 3,094,502, which describe polymerizing acrylonitrile in dimethyl sulfoxide to provide a spinning solution of polyacrylonitrile in the foregoing solvent, followed by extrusion. See also U.S. Pat. No. 3,437,717, which describes the preparation of a film made from a copolymer of acrylonitrile and a polyalkenyl monomer, the film being prepared by dissolving the copolymer in a polar organic solvent such as dimethyl formamide or mixtures of dimethyl formamide with dimethyl sulfoxide, followed by casting the film from the foregoing solution, removing part of the solvent, stretching the film biaxially, and removing most of the remaining solvent by air drying.